U.S. patent number 7,358,954 [Application Number 11/098,085] was granted by the patent office on 2008-04-15 for synchronized light emitting diode backlighting systems and methods for displays.
This patent grant is currently assigned to Cree, Inc.. Invention is credited to Gerald H. Negley, Antony P. van de Ven.
United States Patent |
7,358,954 |
Negley , et al. |
April 15, 2008 |
Synchronized light emitting diode backlighting systems and methods
for displays
Abstract
A display screen includes at least two arrays of at least two
different color picture elements. A backlighting system for the
display includes at least two arrays of Light Emitting Diode (LED)
devices that are configured to radiate light of at least two colors
in a light path that impinges on the display screen, to provide
backlighting on the display screen. A synchronizer is configured to
synchronously activate and deactivate at least a first one of the
arrays of LED devices and at least a first one of the arrays of
color picture elements. Different arrays of synchronously activated
and deactivated LED devices and color picture elements also may be
alternatingly synchronously activated and deactivated. The
backlighting also may be pulsed.
Inventors: |
Negley; Gerald H.
(Hillsborough, NC), van de Ven; Antony P. (Sai Kung,
HK) |
Assignee: |
Cree, Inc. (Durham,
NC)
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Family
ID: |
36239634 |
Appl.
No.: |
11/098,085 |
Filed: |
April 4, 2005 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20060221044 A1 |
Oct 5, 2006 |
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Current U.S.
Class: |
345/102;
345/87 |
Current CPC
Class: |
G09G
3/3413 (20130101); G09G 3/342 (20130101); G09G
3/3607 (20130101); G09G 2310/0235 (20130101); G09G
2310/0237 (20130101); G09G 2310/024 (20130101); G09G
2320/02 (20130101) |
Current International
Class: |
G09G
3/36 (20060101) |
Field of
Search: |
;345/102 ;315/61,69 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1 380 876 |
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Jan 2004 |
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EP |
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4-159519 |
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Jun 1992 |
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JP |
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9-146089 |
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Jun 1997 |
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JP |
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WO 99/66483 |
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Dec 1999 |
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WO |
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WO 01/43113 |
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Jun 2001 |
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WO |
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WO 03/056876 |
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Jul 2003 |
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WO |
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WO 03/056876 |
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Jul 2003 |
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WO |
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WO 03/091771 |
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Nov 2003 |
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WO |
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Other References
Negley, "Reflective Optical Elements for Semiconductor Light
Emitting Devices", U.S. Appl. No. 10/898,608, filed Jul. 23, 2004.
cited by other .
Negley et al., "Light Emitting Diode Arrays for Direct Backlighting
by Liquid Crystal Displays", U.S. Appl. No. 11/022,332, filed Dec.
23, 2004. cited by other .
Negley et al., "Light Emitting Diode Backlighting Systems and
Methods That Use More Colors Than Display Picture Elements", U.S.
Appl. No. 11/098,126, filed Apr. 4, 2005. cited by other .
International Search Report, PCT International Application No.
PCT/US2006/001220; Jan. 26, 2007. cited by other .
Invitation to Pay Additional Fees and Partial Search Report, PCT
International Application No. PCT/US2006/001220; Jun. 6, 2006.
cited by other .
Notification of Transmittal of the International Search Report and
the Written Opinion of the Intenational Searching Authority, or the
Declaration, International Search Report, and Written Opinion of
the International Searching Authority, PCT International
Application No. PCT/US2006/002117, May 30, 2006. cited by other
.
Notification of Transmittal of the International Search Report and
the Written Opinion of the International Searching Authority, or
the Declaration, International Search Report, and Written Opinion
of the International Searching Authority, PCT International
Application No. PCT/US2005/044805, May 9, 2006. cited by
other.
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Primary Examiner: Eisen; Alexander
Assistant Examiner: Lee; Kenneth B
Attorney, Agent or Firm: Myers Bigel Sibley & Sajovec,
P.A.
Claims
What is claimed is:
1. A backlight system for a display screen that includes an array
of Liquid Crystal Display (LCD) devices including arrays of red,
green and blue color filters thereon to provide red, blue and green
color picture elements, the backlight system comprising: arrays of
red, green, blue and cyanine Light Emitting Diode (LED) devices
that are configured to radiate light of red, green, blue and
cyanine colors in a light path that impinges on the display screen
to provide backlighting on the display screen; and a synchronizer
that is configured to synchronously activate and deactivate the
arrays of green and blue LED devices and the arrays of green and
blue color picture elements and to alternatingly synchronously
activate and deactivate the array of cyanine LED devices and the
arrays of red, green and blue color picture elements.
2. A backlight system according to claim 1 wherein the synchronizer
is configured to activate and deactivate at least a first one of
the arrays of LED devices multiple times in synchronism with a
single activation and deactivation of at least a first one of the
arrays of color picture elements.
3. A backlight system according to claim 1 wherein the synchronizer
is configured to pulse at least a first one of the arrays of LED
devices multiple times in synchronism with a single activation and
deactivation of at least a first one of the arrays of color picture
elements.
4. A backlight system according to claim 1 further comprising an
array of amber LED devices that is configured to radiate light of
amber color in the light path that impinges on the display screen
to provide backlighting on the display screen and wherein the
synchronizer is further configured to synchronously activate and
deactivate the arrays of green and blue LED devices and the arrays
of green and blue color picture elements and to alternatingly
synchronously activate and deactivate the arrays of cyanine and
amber LED devices and the arrays of red, green and blue color
picture elements.
5. A backlight system according to claim 1 wherein the synchronizer
is further configured to synchronously activate and deactivate the
array of green LED devices and the array of green color picture
elements, to alternatingly synchronously activate and deactivate
the array of blue LED devices and the array of blue color picture
elements and to alternatingly synchronously activate and deactivate
the array of cyanine LED devices and the arrays of red, green and
blue color picture elements.
6. A backlight system according to claim 1 further comprising an
array of amber LED devices that is configured to radiate light of
amber color in the light path that impinges on the display screen
to provide backlighting on the display screen and wherein the
synchronizer is configured to synchronously activate and deactivate
the array of green LED devices and the array of green color picture
elements, to alternatingly synchronously activate and deactivate
the array of blue LED devices and the array of blue color picture
elements and to alternatingly synchronously activate and deactivate
the array of cyanine and amber LED devices and the arrays of red,
green and blue color picture elements.
7. A display screen comprising the array of LCD devices including
arrays of red, green and blue color filters thereon and a backlight
system according to claim 1.
8. A method of increasing a color gamut of a display panel that
includes a display screen comprising an array of Liquid Crystal
Display (LCD) devices including arrays of red, green and blue color
filters thereon to provide red, blue and green color picture
elements and arrays of red, green, blue and cyanine Light Emitting
Diode (LED) devices that are configured to radiate light of red,
green, blue and cyanine colors in a light path that impinges on the
display screen to provide backlighting on the display screen, the
method comprising: synchronously activating and deactivating the
arrays of green and blue LED devices and the arrays of green and
blue color picture elements and alternatingly synchronously
activating and deactivating the array of cyanine LED devices and
the arrays of red, green and blue color picture elements.
9. A method according to claim 8 further comprising activating and
deactivating at least a first one of the arrays of LED devices
multiple times in synchronism with a single activation and
deactivation of at least a first one of the arrays of color picture
elements.
10. A method according to claim 8 further comprising pulsing at
least a first one of the arrays of LED devices multiple times in
synchronism with a single activation and deactivation of at least a
first one of the arrays of color picture elements.
11. A method according to claim 8 wherein the display screen
further comprises an array of amber LED devices that is configured
to radiate light of amber color in the light path that impinges on
the display screen to provide backlighting on the display screen
and wherein synchronizing further comprises synchronously
activating and deactivating the arrays of green and blue LED
devices and the arrays of green and blue color picture elements and
alternatingly synchronously activating and deactivating the arrays
of cyanine and amber LED devices and the arrays of red, green and
blue color picture elements.
12. A method according to claim 8 wherein synchronizing further
comprises synchronously activating and deactivating the array of
green LED devices and the array of green color picture elements,
alternatingly synchronously activating and deactivating the array
of blue LED devices and the array of blue color picture elements
and alternatingly synchronously activating and deactivating the
array of cyanine LED devices and the arrays of red, green and blue
color picture elements.
Description
FIELD OF THE INVENTION
This invention relates to displays such as Liquid Crystal Displays
(LCDs), and more particularly, to backlighting of displays, such as
LCDs.
BACKGROUND OF THE INVENTION
Display screens are widely used for computer monitors, televisions
and many other display applications. Some flat panel display
screens include an array of optical shutters and a backlight system
that impinges light on the display screen.
For example, LCD devices are widely used in flat panel displays for
monitors, televisions and/or other display applications. As is well
known to those having skill in the art, an LCD display generally
includes an array of LCD devices that act as an array of optical
shutters. Transmissive LCD displays employ backlighting using, for
example, fluorescent cold cathode tubes above, beside and sometimes
behind the array of LCD devices. A diffusion panel behind the LCD
devices can be used to redirect and scatter the light evenly to
provide a more uniform display.
Conventional shuttered display devices generally include three
different color picture elements (often referred to as pixels
and/or subpixels), generally red (R), green (G) and blue (B)
picture elements. A backlight system for shuttered display devices
may be configured to uniformly radiate light on the display screen
that provides the appearance of white light.
As is well known to those having skill in the art, the combination
of red, green and blue picture elements define a gamut of colors or
color gamut, which is that portion of the visible color space that
can be represented by the display. The visible color space and a
color gamut therein are generally represented in an x-y
chromaticity diagram. In order to improve the accuracy of images
that can be displayed on the display, it may be generally desirable
to increase the color gamut of a display.
SUMMARY OF THE INVENTION
Backlight systems for display screens that include at least two
arrays of a respective at least two different color picture
elements may be provided, according to various embodiments of the
present invention, by providing at least two arrays of LED devices
that are configured to radiate light of a respective at least two
colors in a light path that impinges on the display screen, to
provide backlighting on the display screen. A synchronizer is
configured to synchronously activate and deactivate at least a
first one of the arrays of LED devices and at least a first one of
the arrays of color picture elements.
In some embodiments, the synchronizer is configured to
synchronously activate and deactivate at least a first one of the
arrays of LED devices and at least a first one of the arrays of
color picture elements, and to alternatingly synchronously activate
and deactivate at least a second one of the arrays of LED devices
and at least a second one of the arrays of color picture elements.
Moreover, in some embodiments, the synchronizer is configured to
activate and deactivate the at least a first one of the arrays of
LED devices multiple times in synchronism with a single activation
and deactivation of the at least a first one of the arrays of color
picture elements. In other embodiments, the synchronizer is
configured to pulse the at least the first one of the arrays of LED
devices multiple times in synchronism with a single activation and
deactivation of at least a first one of the arrays of color picture
elements.
In some embodiments of the present invention, the display screen
that includes at least two arrays of the respective at least two
different color picture elements comprises an array of LCD devices
including at least three color filters thereon. In some
embodiments, the array of LCD devices includes red, green and blue
color filters thereon, to provide red, green and blue color picture
elements, the at least two arrays of LED devices include arrays of
red, green and blue LED devices, and the synchronizer is configured
to synchronously activate the array of green picture elements and
the array of green LED devices. In other embodiments, the
synchronizer is configured to synchronously activate the array of
blue picture elements and the array of blue LED devices. In still
other embodiments, the synchronizer is configured to synchronously
activate and deactivate the array of blue LED devices and the array
of blue color picture elements and to alternatingly synchronously
activate and deactivate the array of green LED devices and the
array of green color picture elements. The red LED devices may be
activated with the green and blue LED devices, or may be
synchronously activated one or the other.
In still other embodiments, the at least two arrays of LED devices
include arrays of red, green, blue and cyanine (also referred to as
cyan) LED devices, and the synchronizer is configured to
synchronously activate and deactivate the arrays of green and blue
LED devices and the arrays of green and blue color picture
elements, and to alternatingly synchronously activate and
deactivate the array of cyanine LED devices and the arrays of red,
green and blue color picture elements. The red LED devices may be
synchronized with the green and blue LED devices or with the
cyanine LED devices, or with both sets.
In yet other embodiments, the at least two arrays of LED devices
include arrays of red, green, blue, cyanine and amber (also
referred to as yellow) LED devices, and the synchronizer is
configured to synchronously activate and deactivate the arrays of
green and blue LED devices and the array of green and blue color
picture elements, to alternatingly synchronously activate and
deactivate the arrays of cyanine and amber LED devices and the
arrays of red, green and blue color picture elements. In still
other embodiments, the synchronizer is configured to synchronously
activate and deactivate the array of green LED devices and the
array of green picture elements, to alternatingly synchronously
activate and deactivate the array of blue LED devices and the array
of blue color picture elements, and to alternatingly synchronously
activate and deactivate the array of cyanine (and, in some
embodiments, amber) LED devices and the arrays of red, green and
blue color picture elements. The red LED devices may be activated
and deactivated with one or more of the LED devices or may remain
on all the time.
It will be understood by those having skill in the art that
embodiments of the present invention have been described above in
terms of backlight systems for display screens and display screens
including backlight systems. However, other embodiments of the
present invention provide analogous methods of increasing the color
gamut of a display panel that includes an array of LCD devices and
at least two color filters thereon, and at least two arrays of LED
devices that are configured to radiate light of a respective at
least two colors in a light path that impinges on the display
screen, to provide backlighting on the display screen. These
methods may include synchronously activating and deactivating at
least a first one of the arrays of LED devices and at least a first
one of the arrays of color picture elements. Various embodiments as
described above may be provided according to these method aspects.
Moreover, embodiments of the invention may be used with arrays of
backlighting light sources other than LEDs, such as field
emitters/phosphor arrays.
Other embodiments of the present invention can provide backlight
systems for display screens that include an array of at least two
different color picture elements. These backlight systems include
an array of pulsating LED devices that are configured to radiate
pulses of light in a light path that impinges on the display
screen, to provide backlighting on the display screen. These
embodiments can reduce image degradation such as blur and/or
flicker on a display panel by pulsing the array of LED devices to
radiate pulses of light in the light path that impinges on the
display screen, to provide pulsed backlighting on the display
screen.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are cross-sectional views of display panels according
to various embodiments of the present invention.
FIGS. 3A and 3B schematically illustrate operation of conventional
non-switched display panels and alternating synchronized activated
display panels according to various embodiments of the present
invention, respectively.
FIG. 4 graphically illustrates color gamuts for conventional
displays and displays with alternating synchronized backlighting
according to various embodiments of the present invention.
FIGS. 5 and 6 are cross-sectional views of display panels according
to various other embodiments of the present invention.
FIG. 7 schematically illustrates operations with alternating RGB
and CY backlighting LEDs according to various embodiments of the
present invention.
FIG. 8 graphically illustrates an NTSC standard color gamut and
color gamuts using alternating synchronized backlighting LEDs
according to other embodiments of the present invention.
FIGS. 9 and 10 are timing diagrams illustrating pulsing of
backlighting LEDs according to various embodiments of the present
invention.
DETAILED DESCRIPTION
The present invention now will be described more fully hereinafter
with reference to the accompanying drawings, in which embodiments
of the invention are shown. However, this invention should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. In the drawings, the
thickness of layers and regions are exaggerated for clarity. Like
numbers refer to like elements throughout. As used herein the term
"and/or" includes any and all combinations of one or more of the
associated listed items and may be abbreviated as "/".
The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, regions,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, regions,
steps, operations, elements, components, and/or groups thereof.
It will be understood that when an element, such as a layer or
region, is referred to as being "on" or extending "onto" another
element, it can be directly on or extend directly onto the other
element or intervening elements may also be present. In contrast,
when an element is referred to as being "directly on" or extending
"directly onto" another element, there are no intervening elements
present. It will also be understood that when an element is
referred to as being "connected" or "coupled" to another element,
it can be directly connected or coupled to the other element or
intervening elements may be present. In contrast, when an element
is referred to as being "directly connected" or "directly coupled"
to another element, there are no intervening elements present.
It will be understood that, although the terms first, second, etc.
may be used herein to describe various elements, components,
regions, layers and/or sections, these elements, materials,
regions, layers and/or sections should not be limited by these
terms. These terms are only used to distinguish one element,
material, region, layer or section from another element, material,
region, layer or section. Thus, a first element, material, region,
layer or section discussed below could be termed a second element,
material, region, layer or section without departing from the
teachings of the present invention.
Furthermore, relative terms, such as "lower", "base", or
"horizontal", and "upper", "top", or "vertical" may be used herein
to describe one element's relationship to another element as
illustrated in the Figures. It will be understood that relative
terms are intended to encompass different orientations of the
device in addition to the orientation depicted in the Figures. For
example, if the device in the Figures is turned over, elements
described as being on the "lower" side of other elements would then
be oriented on "upper" sides of the other elements. The exemplary
term "lower", can therefore, encompasses both an orientation of
"lower" and "upper," depending on the particular orientation of the
figure. Similarly, if the device in one of the figures is turned
over, elements described as "below" or "beneath" other elements
would then be oriented "above" the other elements. The exemplary
terms "below" or "beneath" can, therefore, encompass both an
orientation of above and below. Moreover, the terms "front" and
"back" are used herein to describe opposing outward faces of a flat
panel display. Conventionally, the viewing face is deemed the
front, but the viewing face may also be deemed the back, depending
on orientation.
Embodiments of the present invention are described herein with
reference to cross section illustrations that are schematic
illustrations of idealized embodiments of the present invention. As
such, variations from the shapes of the illustrations as a result,
for example, of manufacturing techniques and/or tolerances, are to
be expected. Thus, embodiments of the present invention should not
be construed as limited to the particular shapes of regions
illustrated herein but are to include deviations in shapes that
result, for example, from manufacturing. For example, a region
illustrated or described as flat may, typically, have rough and/or
nonlinear features. Moreover, sharp angles that are illustrated,
typically, may be rounded. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the precise shape of a region and are not intended to
limit the scope of the present invention.
Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
FIG. 1 is a cross-sectional view of display panels for flat panel
displays that include backlight systems and methods according to
various embodiments of the present invention. As shown in FIG. 1,
these display panels 100 include a display screen 110 that includes
at least two arrays of a respective at least two different color
picture elements, such as three arrays labeled a, b and c in the
display screen 110. A display data system 112 provides data to the
display screen 110 at a predetermined refresh rate or refresh
frequency. The design of a display screen 110 and a display data
system 112 as described in this paragraph is well known to those
having skill in the art and need not be described further
herein.
Still referring to FIG. 1, a backlight system and method 120 for
the display screen 110 includes at least two arrays of LED devices
122, such as three arrays labeled x, y and z in FIG. 1. The at
least two arrays of LED devices 122 are configured to radiate light
of a respective at least two colors in a light path 130 that
impinges on the display screen 110 to provide backlighting on the
display screen 110. It will be understood by those having skill in
the art that the light path 130 is illustrated by parallel arrows
for the sake of clarity, but that, conventionally, light from the
various color LEDs mix in the mixing area between the LEDs and the
display screen 110, to provide relatively uniform backlighting. The
arrays of LED devices may be positioned to provide direct
backlighting of the display screen as described, for example, in
application Ser. No. 11/022,332, filed Dec. 23, 2004, entitled
Light Emitting Diode Arrays For Direct Backlighting Of Liquid
Crystal Displays, to coinventor Negley et al., to provide edge
backlighting of the display screen, as described in application
Ser. No. 10/898,608, filed Jul. 23, 2004, entitled Reflective
Optical Elements for Semiconductor Light Emitting Devices, to
coinventor Negley, and/or in other backlighting arrangements. It
will be understood that the arrays of LED devices x, y, z may have
a smaller pitch than, a larger pitch than, or the same pitch as,
the arrays of picture elements a, b and c.
Still referring to FIG. 1, the backlight system and method 120 also
includes a synchronizer (SYNCH) 140 that is configured to
synchronously activate and deactivate at least a first one of the
arrays of LED devices x, y and/or z, and at least a first one of
the arrays of color picture elements (pixels) a, b and/or c. As
shown in FIG. 1, in some embodiments, the synchronizer
synchronously activates and deactivates LED devices and color
picture elements by synchronizing the LED devices 122 to a signal
114 that is obtained from the display data 112. However, other
techniques of synchronizing may be used by synchronizer 140, for
example by generating a synchronization signal that is applied to
both the display screen 110 and the array of LED devices 122. The
overall design of a synchronizer is well known to those having
skill in the art and need not be described in detail herein.
Various embodiments of synchronizing may be provided according to
exemplary embodiments of the present invention. For example, as
shown in Block 140 of FIG. 1, in embodiment 141, picture elements a
and LEDs x are synchronously activated and deactivated independent
of the other picture elements and LEDs. In a second embodiment 142,
the synchronizer 140 is configured to synchronously activate and
deactivate color picture elements a and LED devices x, and to
alternatingly synchronously activate and deactivate picture
elements b and LED devices y. In a third embodiment 143, picture
elements a and b are synchronously activated and deactivated along
with LEDs x and y and, alternatingly, picture elements c are
synchronously activated and deactivated along with LEDs z.
In a fourth embodiment 144, the synchronizer 140 is configured to
activate and deactivate at least a first one of the arrays of LED
devices (such as x) multiple times in synchronism with a single
activation and deactivation of at least a first one of the arrays
of color picture elements (such as a). The synchronizer may be
configured to pulse the at least a first one of the arrays of LED
devices multiple times, in synchronism with a single activation and
deactivation of the at least a first one of the arrays of color
picture elements. Thus, in embodiment 144, the array of LEDs x is
pulsed twice in synchronism with activation and deactivation of
picture elements a. It will be understood that more than two pulses
also may be provided. In embodiment 145, the LEDs x are pulsed
twice in synchronism with the pixels a and, alternatingly, the LEDs
y are pulsed three times in synchronism with activation of the
pixels b. Embodiment 146 illustrates that pulsed and non-pulsed
modes may be combined, for example by synchronously activating and
deactivating picture elements a and b and LEDs x and y and,
alternatingly, pulsing LEDs z while activating and deactivating
picture elements c. Finally, embodiment 147 illustrates that the
alternating synchronous activation may take place in groups of
three or more and not only in groups of two. It also will be
understood that modes 141-147 are merely illustrative, and that
other modes and combinations and subcombinations of modes 141-147
may be provided according to various embodiments of the present
invention.
FIG. 2 is a block diagram of display panels according to other
embodiments of the present invention. In these embodiments, the
display screen 210 includes a two-dimensional array of LCD devices
212, and at least two color filters 214 thereon. In FIG. 2, three
color filters 214R, 214G and 214B, corresponding to red, green and
blue color filters, are shown. As is well known to those having
skill in the art, the array of LCD devices 212 and the three color
filters 214 define three arrays of three different color picture
elements (pixels). Moreover, the backlight system and method 220
includes arrays of red, green and blue LED devices 222R, 222G and
222B, respectively. In some embodiments, the red LEDs have a center
frequency of about 625 nm, the green LEDs have a center frequency
of about 535 nm, and the blue LEDs have a center frequency of about
460 nm.
In some embodiments, the synchronizer 240 may be configured to
synchronously activate one or more of the arrays of red, green or
blue picture elements and one or more of the arrays of red, green
and blue LED devices. In other embodiments, the synchronizer may be
configured to synchronously activate and deactivate at least a
first one of the arrays of LED devices and at least a first one of
the arrays of color picture elements, and to alternatingly
synchronously activate and deactivate at least a second one of the
arrays of LED devices and at least a second one of the arrays of
color picture elements. Thus, for example, in embodiment 241, the
green picture elements and the green LEDs are synchronously
activated and deactivated. In a second embodiment 242, the blue
LEDs are pulsed multiple times synchronously with activation and
deactivation of the blue pixels. In a third embodiment 243, the
green picture elements and the green LEDs are synchronously
activated and deactivated alternatingly with synchronous activation
and deactivation of the blue picture elements and blue LEDs. In
embodiment 244, the red and blue picture elements and the red and
blue LEDs are synchronously activated and deactivated and,
alternatingly, the green picture elements and green LEDs are
synchronously activated and deactivated. Finally, in embodiment
245, the green LEDs are pulsed multiple times in synchronism with
activation and deactivation of the green pixels and, alternatingly,
the blue LEDs are pulsed multiple times in synchronism with
activation and deactivation of the blue picture elements. It also
will be understood that many other combinations and subcombinations
of synchronization and alternating synchronization, with or without
pulsing, may be provided according to various embodiments of the
present invention.
FIG. 3 schematically illustrates operation of a conventional
non-switched RGB LCD panel. Viewing FIG. 3 from left to right, the
red, green and blue LEDs and their individual LED spectra are
shown. In a mixing area, the backlight is mixed to provide the
resultant spectra as shown. The light then passes through the color
filters, which provide the color transmission spectra as shown. The
LCD pixel or subpixel cells, therefore, provide the individual
output spectra shown. The eye combines the individual colors to
perceive the gamut or range of colors, as shown in FIG. 3.
FIG. 4 schematically illustrates movement of light through an LCD
panel with LED backlighting and a synchronizer according to
embodiments of the present invention, and more specifically
illustrates embodiment 244 of FIG. 2, wherein the red and blue
color filters and LEDs are alternatingly synchronized with the
green color filters and LEDs. Thus, referring to FIG. 4 from left
to right, and referring to the first time (temporal) frame shown at
the top half of FIG. 4, the red and blue LEDs 222R and 222B are
activated along with the red and blue LCD color filters 214R, 214B.
The white box adjacent the red and blue LED color filters 214R,
214B indicate that the LCDs 212 are activated, whereas the black
box adjacent the green color filter 214G indicates that the LCD 212
is turned off. The resultant color output and color gamut is shown
at the top half of FIG. 4 on the right side. Thus, the top half of
FIG. 4 illustrates how a synchronizer can synchronously activate
and deactivate the array of red picture elements and blue picture
elements, and the array of red and blue LEDs.
Still referring to FIG. 4 in an alternate time frame, shown at the
bottom half of FIG. 4, the green LED 222G is activated and
deactivated along with the green color filter 214G. The red and
blue color filters are off, as shown by the black LCDs 212 adjacent
the red and blue color filters. Thus, the bottom half of FIG. 4
illustrates synchronously activating and deactivating the array of
green LED devices and the array of green color picture elements.
Moreover, the top and bottom portions of FIG. 4 illustrate
synchronously activating and deactivating the array of red and blue
LED devices and the array of red and blue color picture elements
and alternatingly synchronously activating and deactivating the
array of green LED devices and the array of green color picture
elements, corresponding to embodiment 244 of FIG. 2. As shown at
the extreme right of FIG. 4, the eye combines the alternating
colors to perceive a larger gamut or range of colors than was shown
in FIG. 3.
FIG. 4 illustrates a standard NTSC color gamut (dashed line) for a
display. FIG. 4 also illustrates (dotted line) a color gamut of a
conventional display panel that includes red, green and royal blue
backlight LEDs (mixed in respective intensities of 105%, 180% and
123%, to provide a gamut that has an area of 120% of the NTSC
gamut). FIG. 4 also illustrates a simulated color gamut (solid
line) that may be provided by multiplexing the red and blue
backlighting LEDs 222R, 222B and the green backlighting LEDs 222G
according to embodiments of the present invention, as was shown in
FIG. 3B and embodiment 244 of FIG. 2. An expanded color gamut is
shown for alternating synchronized backlighting (solid line)
according to embodiments of the invention, compared to the NTSC
color gamut (dashed line) and the conventional display panel gamut
(dotted line).
Some embodiments of the present invention may arise from a
recognition that, by alternating the blue backlighting LED array
222B with the green backlighting LED array 222G, the color filters
214 need not transmit green light at the same time as blue light,
so that the potential overlap among the color filters at any given
time (illustrated in FIG. 3) may be reduced, minimized and/or
substantially eliminated. Bleed through may be reduced, and the
individual color output spectra can be sharpened. Yet, by
alternating the blue array 222B and the green array 222G at a fast
enough rate, backlighting that is perceived as white light may be
provided. Accordingly, for a given configuration of LCD devices
212, color filters 214 and backlighting LEDs 222, the color gamut
may be unexpectedly increased, in some embodiments of the
invention, by alternating the synchronized blue backlighting LEDs
and blue color filters with the green backlighting LEDs and green
color filters. In some embodiments of the present invention, as
described above, the red LEDs/color filters may be
activated/deactivated along with the blue LEDs/color filters. In
still other embodiments, the red LEDs/color filters need not be
alternated, but may be maintained on with the blue and green
LEDs/color filters, as shown by embodiments 245. These embodiments
may arise from a recognition that the red color filters of FIG. 3
may overlap less with the green color filters than the blue color
filters overlap with the green color filters, so that the red color
filters need not be alternated in order to realize the potential
advantage of alternatingly activating and deactivating the blue and
green LEDs. Moreover, in other embodiments, the color gamut may be
reduced or may not be increased as much, but the intensity of the
display may be increased.
FIG. 5 is a cross-sectional view of display panels including
backlight systems and methods according to yet other embodiments of
the present invention. As shown in FIG. 5, the display panel 210
may be configured as was already described in connection with FIG.
2. The backlight system and method 520, however, includes an array
of red, green, blue and cyanine LED devices 522R, 522G, 522B and
522C, respectively. In some embodiments, the cyanine LEDs have a
center frequency of about 495 nm to about 505 nm. As shown in FIG.
5, a synchronizer 540 is configured to synchronously activate and
deactivate the array of green and blue LED devices 522G, 522B and
the array of green and blue color picture elements 214G and 214B,
and to alternatingly synchronously activate and deactivate the
array of cyanine LED devices 522C and arrays of red, green and blue
color picture elements 214R, 214G, 214B, as shown in a first
embodiment 541. In a second embodiment 542, the red LEDs 522R may
be activated and deactivated along with the green and blue LEDs
522G, 522B, but not with the cyanine LEDs 522C. In still other
embodiments 543, pulsing of the green, blue and/or cyanine LEDs
also may be provided. It will be understood by those having skill
in the art that various combinations and subcombinations of
embodiments 541-543 and/or other embodiments may be provided. For
example, three alternating cycles of synchronous activation and
deactivation may be provided.
FIG. 6 is a cross-sectional view of still other embodiments of the
present invention. In embodiments of FIG. 6, the display panel 600
includes backlighting systems and methods 620 having arrays of red,
green, blue, cyan and yellow (also referred to as amber) LEDs,
622R, 622G, 622B, 622C and 622Y. In some embodiments, the yellow
LEDs have a center frequency of about 570 nm. The synchronizer 640
may be configured to synchronize the red, green, blue, cyanine
and/or yellow LEDs with the red, green and/or blue pixels, and
alternate the activation and deactivation of the synchronized red,
green, blue, cyanine and/or yellow LEDs and the red, green and/or
blue pixels. For example, in a first mode 641, the green and blue
pixels 214G, 214B and the green and blue LEDs 622G, 622B are
synchronously activated and deactivated and, alternatingly, the
green and blue pixels 214G, 214B and the cyanine and yellow LEDs
622C, 622Y are activated. The red LEDs 622R and pixels 214R may be
synchronously activated and deactivated in both of the alternating
cycles. In embodiment 642, the red LEDs 622R are only activated and
deactivated in synchronism with the green and blue LEDs 622G, 622B,
and are not activated during the alternating activation of the
cyanine and yellow LEDs 622C, 622Y. Finally, in embodiment 643,
three alternating cycles are provided wherein the green LEDs are
pulsed, the blue LEDs are activated, and the cyanine and yellow
LEDs are activated. The red LEDs may be activated with any or all
of the cycles. It will also be understood that combinations and
subcombinations of modes 641-643 and/or other modes may be provided
according to other embodiments of the present invention.
FIG. 7 schematically illustrates how the color gamut may be
increased by alternating the activation and deactivation of the
synchronized red, green and blue LEDs and LCD picture elements, and
the synchronized cyan and yellow LEDs and the red, green and blue
picture elements. As shown in FIG. 7, in the alternate temporal
frames where the yellow and cyan LEDs are activated, all three LCD
picture elements (red, green and blue) also may be activated.
However, in other embodiments, all three LCD picture elements need
not be activated.
FIG. 8 simulates how the color gamut (solid line) may be increased
compared to the NTSC color gamut (dashed line) by alternating the
RB (actually royal blue (rB)) and green LEDs, and by alternating
the RGB and CY LEDs, as shown in embodiments 244 and 642, where
mixing is performed according to the intensities shown in FIG. 8.
Increased color gamut by alternating activation of arrays of LEDs
is therefore simulated in FIG. 8.
FIGS. 1-2, 3B and 4-8 also illustrate methods of increasing a color
gamut of a display panel according to embodiments of the present
invention, wherein the display panel includes an array of LCD
devices including at least two color filters thereon, and at least
two arrays of LED devices that are configured to radiate light of
the respective at least two colors in a light path that impinges on
the display screen, to provide backlighting on the display screen.
These methods comprise synchronously activating and deactivating at
least a first one of the arrays of LED devices and at least a first
one of the arrays of color picture elements. Various method analogs
of FIGS. 1-2, 3B and 4-8 may be provided. Moreover, in any of the
embodiments of FIGS. 1-2, 3B and 4-8, backlight sources other than
LEDs (such as field emitters) may be used and/or shutterable
displays other than LCDs (such as holographic optical elements) may
be used.
Additional discussion of various embodiments of the present
invention now will be provided. Presently, shutterable displays
(LCD or other types) may not actually depict the true color of
images. The gamut generally is restricted due to the color
chromaticity values of the red, green and blue sources, such as
phosphors in the screen or LCD color filters with a white light
backlit source. Hence, if one displays, for example, a photograph
on a display screen and then prints the photograph on paper, the
print may not match the image on the display screen.
Some embodiments of the present invention can allow improved color
gamut by alternating between blue and green; between green and blue
and cyanine; between blue/green and cyanine; between green/blue and
cyanine/yellow; and/or between blue and green and cyanine/yellow
backlighting, due to the overlap and bleed-through of a standard
filter system. By allowing improved color gamut, the image may be
better rendered on the display. Red can be on all the time or can
be alternated.
In some embodiments, the blue color filter is used for the blue
backlight source or the cyanine backlight source, so that these
backlight sources are alternated (blue on, cyanine off, and cyanine
on, blue off). Additionally, since the green filter is used for the
green backlight source and the amber or yellow backlight source,
these also can be alternated (green on, amber off, and amber on,
green off). The red backlight LED may be on all the time or can be
alternated with either backlight source(s).
Using a series of pulses to reduce visual flicker, according to
various embodiments of the present invention, now will be
described. In particular, images generally are presented on
television and computer monitors as a series of image frames. The
frequency that the image is refreshed generally is selected to be
greater than the human visual system's "critical flicker
frequency". For television, this frequency is generally either 50
or 60 Hz. For computer monitors, higher frequencies, such as 75 Hz
are sometimes selected to reduce eye strain. For film-type motion
pictures, images are presented at 24 frames per second. To remove
the flicker of 24 Hz, each image is presented twice by interrupting
the light source at a frequency of 48 Hz. This interruption "fools"
the human visual system and the images perceived with flicker,
because it is presented at an apparent 48 Hz.
LCD shutters may take up to 16 ms to change state. While a 16 ms
refresh time may be sufficient to present the individual frames
without flicker, the change is not instantaneous and moving images
may tend to blur. This blur can be reduced by using more
sophisticated and potentially expensive LCD materials and/or
technologies. Such materials may have switching times as fast as 8
ms. However, some perceivable blur still may be present. Another
way to potentially reduce this blur is to pre-bias the LCD ahead of
the change, so that it is "ready" to change. However, pre-biasing
may use special driving circuits. Re-biasing may be used today in
advanced LCD televisions.
According to some embodiments of the present invention, another way
to reduce this blur is to pulse the backlight such that it is only
illuminated for a small portion of the refresh cycle. This pulsing
may be performed because the LED can have near instantaneous switch
times. FIG. 9 graphically illustrates the image data (a), the LCD
pixels (b) with the relatively slow switching time, a pulsed LED
backlight (c), the resultant output (d) and the visual effect (e).
Moving images, therefore, may seem less blurred. The brightness
intensity lost due to reducing the time the backlight is
illuminated can be compensated by increasing the drive current of
the LEDs when they are illuminated, so that the average
illumination can be made the same. Accordingly, some embodiments of
the present invention can reduce image degradation such as blur
and/or flicker of a display panel that includes a display screen
comprising an array of at least two different color picture
elements and an array of LED devices that are configured to radiate
light in a light path that impinges on the display screen to
provide backlighting on a display screen, by pulsing the array of
LED devices to radiate pulses of light in the light path that
impinges on the display screen to provide pulse backlighting on the
display screen.
According to other embodiments of the invention, pulse backlighting
may be combined with alternating backlighting, as was described in
connection with, for example, embodiments 144, 145, 146, 242, 245,
543 and 643. More specifically, when alternating LCD frames in the
color domain according to embodiments of the present invention, it
may be desirable to provide a full LCD switching time in each color
frame. While a switching frequency of about 200 Hz may be
desirable, conventional LCDs may only be able to switch at 60 Hz.
With a 60 Hz refresh rate and a color alternation of 2, as shown,
for example, in FIGS. 3B and 7, the presented image may flicker at
30 Hz.
Using an LCD with a higher switch frequency may reduce this
flicker. For example, an LCD with a switching time of 10 ms can
display a two-frame color multiplexed image at 50 Hz. However, even
50 Hz may provide a barely acceptable refresh rate.
In contrast, according to embodiments of the present invention,
during selected or each color frame of the alternating sequence,
the backlight is pulsed with a series of two or more pulses. The
flicker can be reduced such that even standard 16 ms LCDs can be
used.
FIG. 10 graphically illustrates pulsing of alternating groups of
LCDs according to embodiments of the present invention. Embodiments
642 are illustrated. The alternating CY and RGB LCD cells are shown
at (a) and the pulsing backlight is shown at (b) for the CY LEDs
and at (c) for the RGB LEDs. The total output is shown at (d).
Pulsing according to embodiments of the present invention can,
therefore, allow reduced flicker and eye strain, allow reduced blur
from moving images and/or allow the use of cheaper 16 ms LCDs in
color multiplex applications for a wide gamut.
It also will be understood by those having skill in the art that
various combinations and subcombinations of embodiments of FIGS.
1-2, 3B and 4-10 may be provided according to various other
embodiments of the present invention.
In the drawings and specification, there have been disclosed
embodiments of the invention and, although specific terms are
employed, they are used in a generic and descriptive sense only and
not for purposes of limitation, the scope of the invention being
set forth in the following claims.
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